You have to factor in that DC has to pay people to make the comics. So it is not like DC publishes two comics at no cost. They may have been making a profit, but was it substantial, all things considered?

Also, Hal Jordan was wandering from place to place and job to job before Denny O'Neil started writing him. That is how places like Evergreen City and characters like Eve Doreamus came about. I think Morrison is inspired more so by that period than the O'Neil era.

There's really no other newer era to draw upon. The tiny bit of civilian Hal stuff in the beginning of Vol. 3? Geoff Johns having him be a hotshot pilot with a girlfriend who he forgot about for a few issues in Vol. 4, before losing interest in that?

Well here's the thing - Simon and Jessica were never that interesting to begin with. The diversity thing can only get you along so far, after a while the characters need to be compelling and the story more exciting than "generic space bad guy."
Continuing from there, there are simply too many human/Earth Lanterns. What are we at now? 7? It's just gotten watered down. It's time to phase Simon and Jessica out. The experiment didn't pan out. It happens. Let's move on.

Now that all is said and done, In my opinion, the "Rebirth" Green Lantern books were a big waste of time. They were either badly done on top of being bad ideas (Green Lanterns), or were just... a whole lot of nothing (Hal Jordan and the Green Lantern Corps).